The invention relates to a process and apparatus for three-dimensional position control of the focal point of a high-energy laser, which allows for measurement of directional deviation as well as the focal-distance deviation of the laser beam.
When laser beams are used in processing a material, it is necessary that the beam be positioned and focussed as precisely as possible. Numerous suggestions have been made in order to achieve this purpose. For example, German Patent Document DE 32 02 432 C2 discloses a system which uses a second laser beam and, while monitoring the target, corrects the position in the plane perpendicularly to the beam, but not the depth of the focal point. The same is true for the arrangement according to German Patent Document DE 34 06 677 A1. German Patent Document DE 38 00 427 A1 discloses an arrangement to control the distance of the laser from the workpiece, the focus being determined by means of a detector element consisting of two separate halves.
It is an object of the invention to provide a process and apparatus to determine during the working operation, not only the directional deviation of the beam in a plane perpendicular to the beam axis but also the deviation of the focal point along the beam axis, irrespective of the surface characteristics of the material to be worked, and as a result permit a position control during the working operation.
This and other objects and advantages are achieved according to the invention, in which a beam splitter is utilized to split off a portion of the energy of the laser beam, and such split off portion is then focussed on a quadrant detector by means of an optical system which introduces an astigmatic aberration. The various patterns and pattern positions generated on the quadrant detector are then analyzed in an electronic circuit to generate control signals to control the main laser beam.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.